A Highly Conductive, Self-Recoverable, and Strong Eutectogel of a Deep Eutectic Solvent with Polymer Crystalline Domain Regulation

A functional eutectogel based on ultrahigh-molecular weight polymers: Physical entanglements in deep eutectic solvent

Eutectogels have emerged as a promising material for wearable devices due to its superior ionic conductivity, non-volatility, and low cost. Despite numerous efforts, only a limited number of polymers and gelling mechanisms have been successfully employed in the fabrication of eutectogels. In this study, an effective three-dimensional network is developed based on the entanglements of polymer chains, facilitating the formation of an entangled eutectogel. The fabrication process involves directly dissolving ultra-high molecular weight polyvinylpyrrolidone (PVP) in deep eutectic solvent (reline) through a simple heating-cooling method. The resulting eutectogel, containing 40 wt% PVP, exhibits excellent stretchability of 1410 % strain, toughness of 544.8 kJ/m3, and ionic conductivity of 0.015 S/m. It also generates a reliable resistance signal suitable for strain-sensing applications. Furthermore, this entangled eutectogel displays self-healing capabilities, enabled by the diffusion and re-entanglement of polymer chains. This work not only demonstrates a facile fabrication approach for an entangled eutectogel but also provides the first investigation into employing long chain entanglements in the development of eutectogels.

Lignin-enabled ultra-stretchable eutectic gels for multifunctional sensors

Eutectic gels as important conductive polymers have promising practical applications in wearable electronic devices. However, the development of the ultra-stretchable and self-adhesive eutectic gel for multifunctional flexible sensors remains a challenge. Here, a lignin-enabled ultra-stretchable eutectic gel (LEG) integrating with excellent self-adhesion and high conductivity is prepared through polymerizable deep eutectic solvents (PDES) treated lignin followed by in-situ polymerization. In this LEG, the lignin macromolecules are utilized as important mediators to build dynamic crosslinking points in the polyacrylic acid (PAA) networks via hydrogen bond interactions. The dynamic disruption and reconstruction of the hydrogen bonds between the mobile PAA chain and dynamic crosslinking points ensure the high integrity of the crosslinking network to realize the ultra-stretchability (about 4845 %). Additionally, the abundant phenol groups of lignin endow the LEG with robust self-adhesion, which allows the LEG to seamlessly adhere to the different substrates. Based on these features, the LEGs are assembled as wearable strain sensors with high sensitivity, fast response time, and long-term sensing stability, and this wearable strain sensor demonstrates promising applications in human motion monitoring and information encryption systems. This work develops an effective pathway to design lignin-enabled ultra-stretchable eutectic gels for multifunctional sensors.

Highly Stretchable, Tough, and Transparent Chitin Nanofiber-Reinforced Multifunctional Eutectogels for Self-Powered Wearable Sensors

Traditional conductive hydrogels have disadvantages for wearable sensors, such as poor electrical conductivity, weak mechanical properties, narrow application temperature range, and required external power supply, which limit their wide application. However, manufacturing hydrogel sensors with excellent mechanical properties and self-adhesive, temperature-resistant, and self-powered properties remains a challenge. Herein, chitin nanofiber-reinforced eutectogels (CAANF) with self-adhesive, self-healing, transparent, environment tolerant, and good mechanical properties were obtained via a simple one-pot method with the deep eutectic solvent (DES) system composed of acrylic acid, acrylamide, and choline chloride (ChCl). High-density hydrogen bond networks between CAANFs can act as strong cross-linking sites, conferring high stretchability (1680%) and elasticity. Moreover, high-density hydrogen bond networks with dynamic reversibility can provide excellent self-healing and adhesion abilities. Due to the unique properties of DES, CAANF eutectic gels also exhibit good ionic conductivity and environmental resistance, allowing the sensor to be applied over a wide temperature range (-30 to 60 °C). Additionally, CAANF-based self-powered flexible sensors can be used to detect human movement, monitor health status, and transmit signals for the encryption and decryption of information according to the Morse code. This work expands the scope of portable applications in the field of wearable electronic devices.

Green Manufacture of Hydrated Polymers Coatings with On-Demand Mechanics and Lubricity Based on Novel Biobased Polymerizable Deep Eutectic Solvents

The aging population necessitates a critical need for medical devices, where polymers-based surface lubrication coating is essential for optimal functionality. In fact, lubrication and mechanical requirements vary depending on the service environment of different medical devices. Until now, key mean is still blank for general preparation of hydrophilic polymers-based lubrication coatings with on-demand mechanics and lubricity. This study introduces a novel hydrophilic lubrication coating with tunable mechanical properties and lubricity, derived from eco-friendly polymerizable deep eutectic solvents (PDESs) containing betaine, hydroxyethyl acrylate, glycerol, and tannic acid. Unlike traditional high molecular weight polymers, this approach leverages small-molecule, high-biobased PDESs, thereby simplifying the synthesis process. The resulting coating demonstrates exceptional adhesion to a range of medical device materials─including glass, stainless steel, polyvinyl chloride, and polyurethane─thanks to the high content of hydroxyl groups and pyrogallol motifs from tannic acid. It also enables the precise tuning of mechanical strength, modulus, adhesion, hydrophilicity, and lubrication properties by varying the amounts of glycerol and tannic acid. Furthermore, the coating undergoes a hydration-induced transition from high-strength, high-friction to low-strength, low-friction states, maintaining repeatable performance. Additionally, the synergistic effects of betaine and tannic acid in the PDES contribute to its notable antimicrobial properties. In summary, these PDESs demonstrate significant potential for enhancing lubrication in a range of biomedical devices.

Controlled PVA Release from Chemical-Physical Interpenetrating Networks to Treat Dry Eyes

Dry eye disease is becoming increasingly prevalent, and lubricating eye drops, a mainstay of its treatment, have a short duration of time on the ocular surface. Although there are various drug delivery methods to increase the ocular surface residence time of a topical lubricant, the main problem is the burst release from these delivery systems. To overcome this limitation, herein, a chemical-physical interpenetrating network (IPN) was fabricated to take control over the release of poly(vinyl alcohol) (PVA), a well-known therapeutic agent used to stabilize tear film, from gelatin methacrylate (GelMA) hydrogels. In this report, PVA was specifically used as part of a GelMA-based polymeric hydrogel owing to its physical cross-linking ability via a simple freeze-thaw method. The interpenetrating polymer network was fabricated in a sequential manner where GelMA was chemically cross-linked by photo-cross-linking, followed by physical cross-linking of PVA using a relatively short freeze-thaw cycle. Interestingly, upon applying only one short freeze-thaw cycle (of 1 or 2 h), the crystalline domains in PVA were increased in the interpenetrating network. The endothermic peaks at 48 and 60 °C in differential scanning calorimetry (DSC) thermograms and 20°-2θ peaks in X-ray diffraction (XRD) patterns suggest the presence of these crystalline domains. With the help of a suite of characterization, we further delineate the role of freeze-thaw cycles in taking control over the release of PVA. The release profiles of the PVA-containing hydrogels showed highest linearity with the Korsmeyer-Peppas model (0.9944 < R 2 < 0.9952), indicating that these systems follow non-Fickian or anomalous transport.

Cationic chitosan enables eutectogels with high ionic conductivity for multifunctional applications in energy harvesting and storage

Eutectogels are popular as an emerging material in the field of flexible electronics. However, limited mechanical properties and ionic conductivity restrict their multifunctional application expansion. Herein, cationic chitosan quaternary ammonium salt (CQS) was evenly embedded into the three-dimensional porous framework of eutectogel to build ion migration channels. And a simple solvent replacement process enhanced the crystallization of polyvinyl alcohol matrix and hydrogen bonding, preparing composite eutectogels with high toughness, environmental tolerance and conductivity. The prepared gel exhibites excellent mechanical properties (1.72 MPa, 413 %) and conductivity (0.40 S·m-1). Under external force, three-dimensional porous network with cationic polysaccharide distribution can achieve effective piezoionic effect. Moderate CQS significantly enhances the piezoionic voltage output to 270 mV, which is 4.5 times that of the pure eutectogel. Further, the prepared composite eutectogels was used for capacitor energy storage and wearable sensing devices, and has good charge/discharge stability (94 % capacitance retention) and fast response time (292 ms). This design is typically suitable for preparing advanced multifunctional ion conductors using various natural polysaccharides with sustainable application potential.

Applications of Functional Polymeric Eutectogels

Over the past two decades, deep eutectic solvents (DESs) have captured significant attention as an emergent class of solvents that have unique properties and applications in differing fields of chemistry. One area where DES systems find utility is the design of polymeric gels, often referred to as "eutectogels," which can be prepared either using a DES to replace a traditional solvent, or where monomers form part of the DES themselves. Due to the extensive network of intramolecular interactions (e.g., hydrogen bonding) and ionic species that exist in DES systems, polymeric eutectogels often possess appealing material properties-high adhesive strength, tuneable viscosity, rapid polymerization kinetics, good conductivity, as well as high strength and flexibility. In addition, non-covalent crosslinking approaches are possible due to the inherent interactions that exist in these materials. This review considers several key applications of polymeric eutectogels, including organic electronics, wearable sensor technologies, 3D printing resins, adhesives, and a range of various biomedical applications. The design, synthesis, and properties of these eutectogels are discussed, in addition to the advantages of this synthetic approach in comparison to traditional gel design. Perspectives on the future directions of this field are also highlighted.

"Dissolve-on-Demand" 3D Printed Materials: Polymerizable Eutectics for Generating High Modulus, Thermoresponsive and Photoswitchable Eutectogels

Solvent-free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N-isopropylacrylamide (NIPAM), acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo-DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)-based 3D printing resin. Due to the hydrogen-bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents.

Nanolignin-Facilitated Robust Hydrogels

Recently, certain challenges and accompanying drawbacks have emerged in the preparation of high-strength and tough polymer hydrogels. Insights from wood science highlight the role of the intertwined molecular structure of lignin and crystalline cellulose in contributing to wood's strength. Herein, we immersed prestretched poly(vinyl alcohol) (PVA) polymer hydrogels into a solution of nanosized lignosulfonate sodium (LS), a water-soluble anionic polyelectrolyte, to creatively reconstruct this similar structure at the molecular scale in hydrogels. The nanosized LS effectively fixed and bundled the prestretched PVA polymers while inducing the formation of dense crystalline domains within the polymer matrix. Consequently, the interwoven structure of crystalline PVA and LS conferred good strength to the composite hydrogels, exhibiting a tensile strength of up to ∼23 MPa, a fracture strain of ∼350%, Young's modulus of ∼17 MPa, toughness of ∼47 MJ/m3, and fracture energy of ∼42 kJ/m2. This hydrogel far outperformed previous hydrogels composed directly of lignin and PVA (tensile strength <1.5 MPa). Additionally, the composite hydrogels demonstrated excellent antifreezing properties (<-80 °C). Notably, the LS-assisted reconstruction technology offers opportunities for the secondary fixation of PVA hydrogel shapes and high-strength welding of hydrogel components. This work introduces an approach for the high-value utilization of LS, a green byproduct of pulp production. LS's profound biomimetic strategy will be applied in multifunctional hydrogel fields.

Zwitterionic Eutectogels with High Ionic Conductivity for Environmentally Tolerant and Self-Healing Triboelectric Nanogenerators

Eutectogels have garnered considerable attention for the development of wearable devices, owing to their inherent mechanical elasticity, ionic conductivity, affordability, and environmental compatibility. However, the low conductivity of existing eutectogels has impeded their progression in electronic applications. Here, we report a zwitterionic eutectogel with an impressive ionic conductivity of up to 15.7 mS cm-1. The incorporation of zwitterionic groups into the eutectogel creates ample mobile charges by dissociating the cation and anion of solvents, thereby yielding exceptional ionic conductivity. Moreover, the abundant electrostatic and hydrogen bonding interactions within the eutectogel endow it with prominent self-healing and adhesive properties. By integrating the eutectogel with a roughly patterned polydimethylsiloxane film, we have successfully constructed a triboelectric nanogenerator (TENG) with a maximum output power density of 112 mW m-2. This TENG is capable of generating stable electrical signals even in extreme temperature conditions ranging from -80 to 100 °C and effectively powering electronic devices. Furthermore, the assembled TENG displays high sensitivity as a self-powered sensor, enabling real-time and precise monitoring of signals derived from human motions. This study establishes a promising approach for the development of sustainable and multifunctional flexible electronics that are resilient in extreme environments.

Conductive Hyaluronic Acid/Deep Eutectic Solvent Composite Hydrogel as a Wound Dressing for Promoting Skin Burn Healing Under Electrical Stimulation

Burns can cause severe damage to the skin due to bacterial infection and severe inflammation. Although conductive hydrogels as electroactive burn-wound dressings achieve remarkable effects on accelerating wound healing, issues such as imbalance between their high conductivity and mechanical properties, easy dehydration, and low transparency must be addressed. Herein, a double-network conductive eutectogel is fabricated by integrating polymerizable deep eutectic solvents (PDESs)including acrylamide/choline chloride/glycerol (acrylamide-polymerization crosslink) and thiolated hyaluronic acid (disulfide-bonding crosslink). The introduction of PDESs provides the eutectogel with a conductivity (up to 0.25 S·m-1) and mechanical strength (tensile strain of 59-77%) simulating those of natural human skin, as well as satisfactory tissue adhesiveness, self-healing ability, and antibacterial properties. When combined with exogenous electrical stimulation, the conductive eutectogel exhibits the ability to reduce inflammation, stimulate cell proliferation and migration, promote collagen deposition and angiogenesis, and facilitate skin tissue remodeling. This conductive eutectogel shows great potential as a dressing for healing major burn wounds.

Lithium-Ion-Doped Eutectogel for Surface-Capacitive Sensing Touch Panel

Touch panels are deemed as a critical platform for the future of human--computer interaction. Recently, flexible touch panels have attracted much attention due to their superior adhesivity and integratability to the human body. However, hydrogel- or organogel-based devices suffer from instability due to liquid evaporation or low-conductivity substrates. It demands an alternative functional touch panel featuring temperature tolerance, high conductivity, and stretchability. Here, we introduce an eutectogel by immobilizing a novel deep eutectic solvent (DES) within 2-hydroxyethyl acrylate (HEA) covalently cross-linked polymer scaffolds. In this DES (ethylene carbonate(EC)-LiTFSI), the C═O group of EC is unique as an electron donor exhibiting strong coordination interactions with Li+, promoting the dissociation of Li+ from LiTFSI to achieve excellent conductivity. Benefiting from their traits, eutectogel presents high conductivity, transmittance, antifreezing, and mechanical strength. In addition, using the surface-capacitive sensing mechanism, the eutectogel can be designed as a 1D strip and 2D rectangular touch panel which can achieve high-resolution touching tracks, even in a low-temperature environment and pressure-then-recovered state. This eutectogel strategy is envisioned to facilitate the development of next-generation intelligent devices, especially in extreme stretching and low-temperature application scenarios.

A universal solvent-replacement strategy to convert alginate hydrogels into mechanically strong and transparent alginate eutectogels for sensitive strain sensors

Eutectogels based on natural polymers have attracted significant attention as an alternative to easily dehydrated hydrogels and expensive ionogels in the development of flexible strain sensors. The feasibility of employing eutectogels derived from pure natural polymers could be greatly enhanced if their mechanical properties satisfy the requirements of applications. Herein, alginate eutectogels (AEs) with high mechanical properties (tensile strain 217 % and strength 2.26 MPa at fracture), and excellent transparency (over 90 %) are acquired via CaCl2 inducing ionic crosslinking and subsequent deep eutectic solvents (DESs, composed of glycerol and choline chloride) initiating physical crosslinking with a universal solvent- replacement strategy. Among them, sodium alginate, a natural polysaccharide polymer, is selected as representative supporting scaffolds and forms water-insoluble alginate hydrogels (AHs) in CaCl2 coagulation bath. The exchange of DESs with water of AHs not only restrengthens the polymer network by physical crosslinking, but also endows the obtained AEs with long-term solvent retention and high temperature resistance. In addition, the AEs not only have high reliability but also exhibit better linear sensitivity in a wide strain range (0-200 %). In particular, the AEs display multiple sensitivity to stretching, bending, and human motions, demonstrating feasibility as sensitive strain sensors.

Phase-Segregated Ductile Eutectogels with Ultrahigh Modulus and Toughness for Antidamaging Fabric Perception

Ionogels are extremely soft ionic materials that can undergo large deformation while maintaining their structural and functional integrity. Ductile ionogels can absorb energy and resist fracture under external load, making them an ideal candidate for wearable electronics, soft robotics, and protective gear. However, developing high-modulus ionogels with extreme toughness remains challenging. Here, a facile one-step photopolymerization approach to construct an acrylic acid (AA)-2-hydroxyethylacrylate (HEA)-choline chloride (ChCl) eutectogel (AHCE) with ultrahigh modulus and toughness is reported. With rich hydrogen bonding crosslinks and phase segregation, this gel has a 99.1 MPa Young's modulus and a 70.6 MJ m-3 toughness along with 511.4% elongation, which can lift 12 000 times its weight. These features provide extreme damage resistance and electrical healing ability, offering it a protective and strain-sensitive coating to innovate anticutting fabric with motion detection for human healthcare. The work provides an effective strategy to construct robust ionogel materials and smart wearable electronics for intelligent life.

Multiple physical crosslinked highly adhesive and conductive hydrogels for human motion and electrophysiological signal monitoring

Hydrogel-based flexible electronic devices serve as a next-generation bridge for human-machine interaction and find extensive applications in clinical therapy, military equipment, and wearable devices. However, the mechanical mismatch between hydrogels and human tissues, coupled with the failure of conformal interfaces, hinders the transmission of information between living organisms and flexible devices, which resulted in the instability and low fidelity of signals, especially in the acquisition of electromyographic (EMG) and electrocardiographic (ECG) signals. In this study, we designed an ion-conductive hydrogel (ICHgel) utilizing multiple physical interactions, successfully applied for human motion monitoring and the collection of epidermal physiological signals. By incorporating fumed silica (F-SiO2) nanoparticles and calcium chloride into an interpenetrating network (IPN) composed of polyvinyl alcohol (PVA) and polyacrylamide (AAm)/acrylic acid (AA) chains, the ICHgel exhibited exceptional tunable stretchability (>1450% strain) and conductivity (10.58 ± 0.85 S m-1). Additionally, the outstanding adhesion of the ICHgel proved to be a critical factor for effective communication between epidermal tissues and flexible devices. Demonstrating its capability to acquire stable electromechanical signals, the ICHgel was attached to different parts of the human body. More importantly, as a flexible electrode, the ICHgel outperformed commercial Ag/AgCl electrodes in the collection of ECG and EMG signals. In summary, the synthesized ICHgel with its outstanding conformal interface capabilities and mechanical adaptability paves the way for enhanced human-machine interaction, fostering the development of flexible electronic devices.

One-step Fabrication of Physical Eutectogel with Recyclability: Crystalline Domain Regulation Induced by Microgels

HYPOTHESIS

Despite their non-volatility, low cost, and recyclability, physical eutectogels' appeal is hindered by the intricate fabrication process and the involvement of hazardous chemicals. The network of polyvinyl alcohol (PVA) in deep eutectic solvent (choline chloride and glycerol) might be developed by the addition of microgels of polyacrylic acid (Carbopol).

EXPERIMENTS

Hydrogen-bond interactions between Carbopol and PVA are revealed through Fourier-transform infrared spectroscopy. The impact of microgels on crystalline domains and the polymer network can be observed using X-ray diffraction and scanning electron microscopy. The physical properties of the eutectogel, including mechanical strength and ionic conductivity, are investigated as well. Finally, the strain-sensing ability and remarkable recyclability of the eutectogel are demonstrated.

FINDINGS

The physical eutectogel can be obtained through a one-step fabrication process using only green and low-cost materials. It demonstrates robust strength (1.02 MPa) and remarkable stretchability (1000 % strain). This is attributed to the uniform dispersion of PVA crystalline domains within the deep eutectic solvent, facilitated by the hydrogen bonds and space restriction effects between PVA and Carbopol. Furthermore, the physical eutectogel with recyclability can consistently generate electrical resistance signals, highlighting its potential as a reliable strain sensor.

A eutectogels-catalyzed one-pot multi-component reaction: access to pyridine and chromene derivatives

The demand for a wide array of functional chemicals and materials has experienced a significant surge in tandem with the advancement of civilization. Regrettably, a number of perilous solvents are employed in chemical laboratories and industrial settings, posing significant risks to the well-being of researchers and contributing to environmental degradation through pollution. Eutectogels, which are based on the eutectic concept, may be synthesized by self-assembling or self-polymerization of various components when put under UV irradiation (254 nm). A novel copolymeric deep eutectic solvent (DES) was successfully synthesized, comprising choline chloride (HBA) as the hydrogen bond acceptor, acetamide (HBD) as the hydrogen bond donor, tetraethyl orthosilicate (TEOS), and formic acid. In this study, we present the preparation of four-component ETGs for synthesizing pyridine and chromene derivatives as a reusable catalyst through a multi-component pathway without solvents. The procedure of synthesizing these heterocyclic compounds is free of using toxic solvents and it could be categorized as a green method.

Ultra-Tough and Highly Stretchable Dual-Crosslinked Eutectogel Based on Coordinated and Non-Coordinated Two Types Deep Eutectic Solvent Mixture

Eutectogels are gaining attention in flexible device applications for their superior ionic conductivity, stability, biocompatibility, and cost-effectiveness. However, most existing eutectogels suffer from low strength and toughness. Herein, ultra-tough and highly stretchable polyacrylamide (PAM) eutectogels featuring a dual-crosslinked network comprising chemical cross-linking and physical cross-linking facilitated by metal coordination bonds and hydrogen bonds are developed. This is achieved through a controlled strategy involving polymerization of acrylamide in a coordinated metal salt-type deep eutectic solvent (DES) combined with a non-coordinated choline chloride (ChCl)-type DES mixture. By varying the molar ratio of these two types of DES, exceptional and adjustable mechanical properties of the resulting eutectogel are achieved, including a high tensile strength ranging from 2.9 to 8.2 MPa and elongation at break ranging from 1725 to 747%, at a 70 wt% DES content. Furthermore, the reversible non-covalent crosslinking in these eutectogels enables self-recovery and self-healing capabilities of eutectogels. The prepared eutectogels also exhibit outstanding ionic conductivity (3.56 mS cm-1 ), making them well-suited for use as strain sensors in human motion detection. The toughening strategy is universally effective for creating tough eutectogels using coordinated metal salt-type DES with various metal ions, as well as a diverse range of coordinatable polymers.

Evolutionary Reinforcement of Polymer Networks: A Stepwise-Enhanced Strategy for Ultrarobust Eutectogels

Gel materials are appealing due to their diverse applications in biomedicine, soft electronics, sensors, and actuators. Nevertheless, the existing synthetic gels are often plagued by feeble network structures and inherent defects associated with solvents, which compromise their mechanical load-bearing capacity and cast persistent doubts about their reliability. Herein, combined with attractive deep eutectic solvent (DES), a stepwise-enhanced strategy is presented to fabricate ultrarobust eutectogels. It focuses on the continuous modulation and optimization of polymer networks through complementary annealing and solvent exchange processes, which drives a progressive increase in both quantity and mass of the interconnected polymer chains at microscopic scale, hence contributing to the evolutionary enhancement of network structure. The resultant eutectogel exhibits superb mechanical properties, including record-breaking strength (31.8 MPa), toughness (76.0 MJ m-3 ), and Young's modulus (25.6 MPa), together with exceptional resistance ability to tear and crack propagation. Moreover, this eutectogel is able to be further programmed through photolithography to in situ create patterned eutectogel for imparting specific functionalities. Enhanced by its broad applicability to various DES combinations, this stepwise-enhanced strategy is poised to serve as a crucial template and methodology for the future development of robust gels.

Facile Solvent Regulation for Highly Strong and Tough Physical Eutectogels with Remarkable Strain Sensitivity

Physical eutectogels have great potential for applications in many fields due to their electrical conductivity, broad temperature stability, and biocompatibility. However, the preparation of high-performance physical eutectogels in a simple, efficient, and cost-effective way remains a challenge. In this study, a facile but efficient solvent regulation strategy was proposed to construct a highly robust poly(vinyl alcohol) (PVA) physical eutectogel. Hydrogen bonds within the polymer-containing deep eutectic solvent system were dynamically regulated by the introduction-removal of water to induce the formation of a uniform and dense polymer cross-linked network, which imparted excellent mechanical properties to the resulting eutectogel. For the eutectogel with 15 wt % PVA, the tensile strength and toughness were 1.67 MPa and 6.81 MJ m-3, respectively, which were at a high level among existing physical eutectogels. This high-performance eutectogel was available as a strain sensor and exhibited high sensitivity. In addition, this eutectogel can be endowed with a directional muscle-like stretching performance through convenient mechanical training. The easy scalability and low cost made our method an effective strategy for developing high-performance physical eutectogels, which would further promote the application of such materials in areas such as wearable electronics and soft robotics.

Efficient Fabrication of TPU/MXene/Tungsten Disulfide Fibers with Ultra-Fast Response for Human Respiratory Pattern Recognition and Disease Diagnosis via Deep Learning

Flexible wearable pressure sensors have received increasing attention as the potential application of flexible wearable devices in human health monitoring and artificial intelligence. However, the complex and expensive process of the conductive filler has limited its practical production and application on a large scale to a certain extent. This study presents a kind of piezoresistive sensor by sinking nonwoven fabrics (NWFs) into tungsten disulfide (WS2) and Ti3C2Tx MXene solutions. With the advantages of a simple production process and practicality, it is conducive to the realization of large-scale production. The assembled flexible pressure sensor exhibits high sensitivity (45.81 kPa-1), wide detection range (0-410 kPa), fast response/recovery time (18/36 ms), and excellent stability and long-term durability (up to 5000 test cycles). Because of the high elastic modulus of MXene and the synergistic effect between WS2 and MXene, the detection range and sensitivity of the piezoresistive pressure sensor are greatly improved, realizing the stable detection of human motion status in all directions. Meanwhile, its high sensitivity at low pressure allows the sensor to accurately detect weak signals such as weak airflow and wrist pulses. In addition, combining the sensor with deep-learning makes it easy to recognize human respiratory patterns with high accuracy, demonstrating its potential impact in the fields of ergonomics and low-cost flexible electronics.

Degradable Supramolecular Eutectogel-Based Ionic Skin with Antibacterial, Adhesive, and Self-Healable Capabilities

The development of degradable, cost-effective, and eco-friendly ionic conductive gels is highly required to reduce electronic waste originating from flexible electronic devices. However, biocompatible, degradable, tough, and durable conductive gels are challenging to achieve. Herein, we develop a facile strategy for the design and synthesis of degradable tough eutectogels by integrating an electrostatically driven supramolecular network composed of branched polyacrylic acid (PAA) and monoethanolamine (MEA) into a green deep eutectic solvent with chitosan quaternary ammonium salt (CQS). The specially designed PAA/MEA/CQS eutectogels present multiple desired properties, including high transparency, widely adjustable mechanical properties, high resilience, reliable adhesiveness, excellent self-healing ability, good conductivity, remarkable anti-freezing performance, and antibacterial properties. The dynamic and reversible supramolecular interactions not only significantly enhance the mechanical properties of the PAA/MEA/CQS eutectogels but also enable fast degradation, addressing the dilemma between mechanical strength and degradability. More importantly, a biocompatible and degradable multifunctional ionic skin is successfully fabricated based on the PAA/MEA/CQS eutectogel, exhibiting high sensitivity, a wide sensing range, and a rapid response speed toward strain, pressure, and temperature. Thus, this study offers a promising strategy for fabricating degradable tough eutectogels, which show great potential as high-performance ionic skins for next-generation flexible wearable electronic devices.

Zwitterionic Eutectogel-Based Wearable Strain Sensor with Superior Stretchability, Self-Healing, Self-Adhesion, and Wide Temperature Tolerance

Ionic conductive eutectogels have great application prospects in wearable strain sensors owing to their temperature tolerance, simplicity, and low cost. Eutectogels prepared by cross-linking polymers have good tensile properties, strong self-healing capacities, and excellent surface-adaptive adhesion. Herein, we emphasize for the first time the potential of zwitterionic deep eutectic solvents (DESs), in which betaine is a hydrogen bond acceptor. Polymeric zwitterionic eutectogels were prepared by directly polymerizing acrylamide in zwitterionic DESs. The obtained eutectogels owned excellent ionic conductivity (0.23 mS cm^-1), superior stretchability (approximately 1400% elongation), self-healing (82.01%), self-adhesion, and wide temperature tolerance. Accordingly, the zwitterionic eutectogel was successfully applied in wearable self-adhesive strain sensors, which can adhere to skins and monitor body motions with high sensitivity and excellent cyclic stability over a wide temperature range (-80 to 80 °C). Moreover, this strain sensor owned an appealing sensing function on bidirectional monitoring. The findings in this work can pave the way for the design of soft materials with versatility and environmental adaptation.

Peptide-enhanced tough, resilient and adhesive eutectogels for highly reliable strain/pressure sensing under extreme conditions

Natural gels and biomimetic hydrogel materials have been able to achieve outstanding integrated mechanical properties due to the gain of natural biological structures. However, nearly every natural biological structure relies on water as solvents or carriers, which limits the possibility in extreme conditions, such as sub-zero temperatures and long-term application. Here, peptide-enhanced eutectic gels were synthesized by introducing α-helical "molecular spring" structure into deep eutectic solvent. The gel takes full advantage of the α-helical structure, achieving high tensile/compression, good resilience, superior fracture toughness, excellent fatigue resistance and strong adhesion, while it also inherits the benefits of the deep eutectic solvent and solves the problems of solvent volatilization and freezing. This enables unprecedentedly long and stable sensing of human motion or mechanical movement. The electrical signal shows almost no drift even after 10,000 deformations for 29 hours or in the -20 °C to 80 °C temperature range.

Deep Eutectic Solvent-Induced Microphase Separation and Entanglement of PVA Chains for Tough and Reprocessable Eutectogels for Sensors

A high-strength PVA-based eutectogel has been synthesized by a strategy of solvent-induced microphase separation. Here, PVA was dissolved in water, and green solvent DES (choline chloride/glycerol) was introduced to induce PVA to undergo microphase separation, leading to poorly solvated domains and highly solvated domains. In poorly solvated domains, the PVA chains were folded and crystallized, and the formed crystalline domains served as physical cross-linkers. Such cross-linking structures endowed the eutectogels with remarkable mechanical properties, showing strength in tension reaching up to 1.2 MPa and elongation at a break of 405%, with rupture toughness of 3.23 MJ m^-3. Meanwhile, the as-obtained eutectogel possessed reprocessability and could be recycled through high-temperature dissolution and recasting. In addition, the eutectogel also exhibited excellent frost resistance, and its ionic conductivity could still reach 0.62 mS cm^-1 at -40 °C. In addition, the eutectogel can maintain a stable output signal during a multiple strain cycle, showing the potential application in the flexible sensor. The eutectogel is capable of detecting the bending movement of joints and identifying the different bending angles of fingers, showing a certain applied potential in motion detection of the human body.